1. Field of the Invention
The present invention relates to a commutator and a brush for a small electric DC motor that carries out electric switching on the basis of mechanical sliding operations, and in particular, to a commutator material and a brush material used for a small electric DC motor to rotate a DVD in a DVD player.
2. Description of the Related Art
In the above technical field, with a shift from CDs to DVDs, many studies have been made on materials for small electric DC motors which are suitable for respective applications. In initial music CD players, a disk rotated at about 500 rpm, which did not impose a heavy load on a commutator or brush material for the small electric DC motor.
CD players subsequently began to be mounted in automobiles as audio instruments. A need thus arose to make the small electric DC motor durable within the temperature range from −40 to 85° C. The applicant thus developed a commutator material for a small electric DC motor which can realize such durability (see Japanese Patent Application Laid-Open No. 8-291349).
The commutator material for a small electric DC motor disclosed in Japanese Patent Application Laid-Open No. 8-291349 can adjust to the increased rotation speeds of CD players such as a double speed and a quadruple speed and to playback-only DVD players. This commutator material is now typical for spindle motors.
However, a method for controlling a spindle motor for a DVD has further been complicated. Consequently, the commutator material for a small electric DC motor described in Japanese Patent Application Laid-Open No. 8-291349 may fail to meet the requirements for the characteristics of the material. Thus, a further improvement in the performance of the material is now demanded. Further, for a further improvement in performance, it is now desirable to develop not only a commutator material for a small electric DC motor but also a brush material used in combination with the commutator material.
In recent years, several schemes for controlling a spindle motor for a DVD have been known. For example, high-grade audio instruments use a pulse current to control the rotational frequency of the motor. However, it has been pointed out that the commutator material for a small electric DC motor described in Japanese Patent Application Laid-Open No. 8-291349 may fail to meet the demand characteristics of the material.
The present invention is made under these circumstances. It is an object of the present invention to provide a commutator material and a brush material for a small electric DC motor which enable a lengthened operating life of a spindle motor for a DVD which is controlled by a pulse current.